In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water and an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An ink jet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-receiving layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
An important characteristic of ink jet recording elements is their need to dry quickly after printing. To this end, porous recording elements have been developed which provide nearly instantaneous drying as long as they have sufficient thickness and pore volume to effectively contain the liquid ink. For example, a porous recording element can be manufactured by cast coating, in which a particulate-containing coating is applied to a support and is dried in contact with a polished smooth surface.
When an ink drop contacts the ink jet recording medium, the drop initially spreads on the surface and then begins to adsorb into the medium. The ink adsorbs vertically into the medium as well as radially. The rate of ink adsorption depends on the nature of the medium. Ink adsorption in non-porous media comprising hydrophilic polymers takes place due to molecular diffusion and occurs at a much slower rate than for porous media where the ink adsorption occurs due to capillary action. The adsorption of the ink drop transports a colorant into the medium to form the image.
The diameter of the resulting colorant in the medium is referred to as dot size. Dot size is an important parameter in ink jet printing systems and is a key component in establishing image quality and printer productivity. Smaller dot sizes yield a gain in edge acuity but decrease printer productivity. Larger dot sizes can cover up for printing errors due to misplaced drops. Therefore, the ability to control dot size is an important issue for ink jet printing systems.
Dot gain refers to the increase in dot size over the initial, spherical drop diameter. The dot gain is determined by the ratio of the final dot diameter to the initial drop diameter. The desired dot size is typically achieved by controlling the drop volume, i.e., larger volume drops produce larger dot sizes in the medium. It would be desirable to find a way to increase dot size without having to increase drop volume.
U.S. Pat. No. 6,114,022 relates to a method for controlling the dot diameter on an ink jet receptive medium that employs a microporous medium and a porous imaging layer. The dot gain achieved by this process is about 3.5. However, there are problems with this method in that the amount of dot gain is not as large as one would like and the process is limited to pigmented inks.
It is an object of this invention to provide a method for increasing the dot gain of an ink jet ink drop applied to an ink jet recording element in an amount of up to about 15. It is another object of the invention to provide a method for increasing the diameter of an ink jet ink dot resulting from the application of an ink jet ink drop wherein the ink jet ink comprises a dye.